The organic electroluminesence diode (OLED) element is composed of a cathode, an anode and a luminance layer. The cathode is made of Al etc. metal material and the anode is made of ITO etc. material. Electrons and holes are respectively injected to the cathode and the anode to form excitons in the organic luminance layer to excite the luminance layer to luminesce. The present product in the laboratory mainly employs a transparent ITO anode. The element structure presents a condition of a top emission. However, in a production line, the ITO is always formed on a bottom, since an ITO deposition damages the organic material. Thus, a structure of a bottom emission is employed and lights are emitted from the cathode.
Currently, most of OLED employ an anode-luminance structure and the cathode is used as a reflection layer, so the cathode reflects environment lights and inside stray lights. In particular, the cathode made of the metal material has high reflectivity to decrease the contrast and sharpness of the OLED. A general solution is to add a ¼ wavelength plate and a polarizer on a light-emitting face of the OLED to improve the reflection problem, but it causes a high cost.